[OPTICAL REVIEW Vol. 14, No. 6 (2007) 384-394]
© 2007 The Optical Society of Japan

A New Algorithm for Die-to-Wafer-like Image Mask Inspection in Real Time

Akira TAKADA1,2*, Toru TOJO1, and Masato SHIBUYA2

1Corporate R&D Center, General Engineering and Quality Assurance Division, Topcon Corporation, 75-1 Hasunuma-cho, Itabashi-ku, Tokyo 174-8580, Japan
2Department of Photonic Information and Media Engineering, Faculty of Engineering, Tokyo Polytechnic University, 1583 Iiyama, Atsugi, Kanagawa 243-0297, Japan

(Received May 31, 2007; Accepted September 10, 2007)

The effect of variations in defect printability must be considered in order to correctly evaluate mask defect inspection procedures. Because of nonlinear transfer effects and strong dependence of printability on defect types, it is difficult to define the boundary between real defect and false defect. To overcome this problem we developed a new algorithm for die-to-wafer-like image (D-to-WI) inspection in real time. This inspection method compares the die (wafer image calculated from CAD data) with the wafer-like image (WI) calculated from the mask image detected by the mask inspection system.
To precisely calculate WI in real time, we developed a new simulation-based software. Since the phase of a mask inspection image cannot be measured, we introduce some assumptions regarding its phase. Moreover, we introduce some corrections for WI such as adding a DC component and multiplying by a proper value. To calculate the die which realizes the desired image with sufficient accuracy in real time, we also introduce a perturbation approach.
We demonstrate numerically the possibility of a new algorithm for D-to-WI inspection. We confirm that this technique of generating WI from a measured mask pattern is well suited for attenuated phase shift masks (PSMs) and Cr binary masks.

Key words: mask, defect, inspection, defect detection sensitivity, algorithm, mask image, wafer image, aerial image, perturbation approach, PSM

*Corresponding author.